Biogas production from Opuntia stricta Haw.: microbial diversity and solid load influence on sludge recycle systems

Abstract

The search for alternative and sustainable energy sources becomes urgent as energy demand increases and fossil fuels become less available, especially in water‐scarce regions such as the Brazilian semi‐arid region, where current projections of global warming and the expansion of arid and semi‐arid zones point to a future of desertification. Prickle pear is a forage Cactaceae adapted to arid environments due to its crassulacean acid metabolism, standing out as a promising plant for biogas production. Its high water use efficiency, low lignin content, and high soluble carbohydrate and mucilage content favor anaerobic digestion without the need for costly pretreatments. The biogas production potential from the anaerobic digestion of the Orelha de Elefante Mexicana variety, cultivated at the Agronomic Institute of Pernambuco, was evaluated through the physical–chemical characterization of the biomass and biochemical methane potential tests, with three organic loads of volatile solids (5, 10, and 15 g VS L ⁻¹ ) over three sequential cycles, creating a recycling‐type experiment. The 5 g VS L ⁻¹ load resulted in the highest biogas yield (0.391 L g ⁻¹ VS ⁻¹ ) and the highest‐quality gas, achieving 63.8% methane in the third cycle. The identification of the predominant microorganisms in the process through metagenomic analysis provided insights into process optimization and a better understanding of the microbial ecology involved. The results highlight the potential of forage cactus as a viable and sustainable alternative for bioenergy generation in the Brazilian semi‐arid region, contributing to the diversification of the regional energy matrix.